In general, the invention relates to protease-resistant mutants of stromal cell derived factor-1 (SDF-1).
DF-1 (also known as CXCL12) is a 68 amino acid member of the chemokine family that is a chemoattractant for resting T-lymphocytes, monocytes, and CD34+ stem cells. SDF-1 is produced in multiple forms: SDF-1α (CXCL12a), SDF-1β (CXCL12b), and SDF-1γ, which are the result of differential mRNA splicing. The sequences of SDF-1α and SDF-1β are essentially the same, except that SDF-1β is extended by four amino acids (Arg-Phe-Lys-Met (SEQ ID NO: 85)) at the C-terminus. The first three exons of SDF-1γ are identical to those of SDF-1α and SDF-1β. The fourth exon of SDF-1γ is located 3200 base-pairs downstream from the third exon on the SDF-1 locus and lies between the third exon and the fourth exon of SDF-1β. SDF-1 is initially made with a signal peptide (21 amino acids in length) that is cleaved to make the active peptide.
SDF-1 plays a key-role in the homing of hematopoietic stem cells to bone marrow during embryonic development and after stem cell transplantation. In addition to its role in stem cell homing, SDF-1 is also important in cardiogenesis and vasculogenesis. SDF-1-deficient mice die perinatally and have defects in cardiac ventricular septal formation, bone marrow hematopoiesis, and organ-specific vasculogenesis. It has also been reported that abnormally low levels of SDF-1 are at least partially responsible for impaired wound healing associated with diabetic patients and that impairment can be reversed by the administration of SDF-1 at the site of tissue damage.
In the normal adult heart, SDF-1 is expressed constitutively, but expression is upregulated within days after myocardial infarction. It has been shown previously that SDF-1 expression increased eight weeks after myocardial infarction by intramyocardial transplantation of stably transfected cardiac fibroblasts overexpressing SDF-1, in combination with G-CSF therapy. This procedure was associated with higher numbers of bone marrow stem cells (c-Kit or CD34+) and endothelial cells in the heart and resulted in an increase of vascular density and an improvement of left ventricular function. These studies suggest that the insufficiency of the naturally-occurring myocardial repair process may be, in part, due to inadequate SDF-1 availability. Hence, the delivery of SDF-1 in a controlled manner after myocardial infarction may attract more progenitor cells and thereby promote tissue repair.
There exists a need in the art for methods and compositions that promote wound healing and tissue repair.